Propellant Depots (An Aside)

While I’ve had to focus all my attention on running the business, and working on our Sticky Boom TRL-raising sprint, there has been a lot of discussion lately about propellant depots, and I wanted to make some quick comments and provide some advanced heads up.

First off, I invented Sticky Booms as a way of solving the depot delivery economics challenge that Josh Hopkins raised a year and a half ago in The Space Review. Josh is a good guy at LM raising a valid point that I feel merited addressing–you can’t close the business case for depots if propellant deliveries require as much overhead as COTS deliveries to the ISS. While trying to formulate a solid, defensible answer to his question, I started thinking about rendezvous and docking in general, and started realizing that Kirk Sorensen’s “Boom Rendezvous” concept might hold part of the answer. While we still have a long way to go, I think that sticky booms have the potential to be a key part in solving that issue. If you can offload most of the prox-ops work onto small upgrades to the launch vehicle upper stage and either a tug or a long sticky boom on the depot itself, the tanker can become a lot simpler–more a dumb tank with some valves and fittings than a space tug in itself like Dragon or Cygnus.

So, while Altius probably isn’t going to be building depots, we’re definitely interested in enabling them, both as customers for sticky booms, but also as a source of demand for stimulating innovation in low-cost launch solutions. I think Norm Augustine hit the nail on the head in his interview that Alan Boyle published today:

It’s kind of like airlines were in the ’30s. They used to be like launch vehicles companies are today. In the ’30s, of course, the government guaranteed that airlines could haul the mail and get contracts. Well, if the government will give contracts to these firms, and guarantee to haul fuel into low Earth orbit, put fueling stations up there and so on, I think they can make a business out of this.

I wish I had the time/bandwidth to participate in proposing to the latest NASA BAA on “Cryostat” development and testing, but am too swamped with Sticky Boom work and proposal work related to Sticky Boom. That said, I’m trying to do my part to support the cause.

One of the objections I’ve been seeing many people raise to propellant depots lately revolves around the orbital dynamics challenges of using them for NEO or Mars missions. I’ve been working with a friend who is a space science mission Flight Director (FIDO in NASA lingo) to start putting together good answers to some of the orbital dynamics issues, and hope to have a chance to blog about this (either here or on Maybe my experience is slanted, but it seems like unmanned science FIDOs tend to be more out-of-the-box thinkers than manned spaceflight FIDOs. If I wasn’t running my own company, I’d love to take some of this work and flesh it out into a paper with him, but will probably have to discuss it quickly in a few short blog posts. The short answer is that so-far it looks like there are many ways of using depots to provide departure opportunities for even challenging NEO missions using LEO propellant depots, it’s just a question of which approach makes the most sense from an economics/physics perspective.

Anyhow, hopefully we’ll get a chance to write up what we’ve found so-far when I get some more free time.

3 Responses
  1. In that same article Norm says that the current path of developing a behemoth HLV is only sensible if you intend to increase NASA’s budget sometime in the future by about $3B/year. Most HLV advocates I have talked to agree with this assessment. The few that don’t are considered naive, even by the HLV advocate community, as it is painfully obvious that NASA doesn’t have the budget to operate a vehicle more expensive than the Shuttle and do multiple missions to the Moon, asteroids, etc.

    This is essentially the argument that the propellant depot crowd has been trying to make for years, but we start the conversation with: well, the NASA budget is never going to increase, so we need to do things smarter.. This immediately puts us on the outs with the HLV crowd because they’re predominately increase-the-budget advocates.

  2. Trent,
    I guess for me, my doubts about NASA getting a budget increase aren’t my only or biggest reason for supporting a depot-centric architecture. For me it’s more of a question of what you get out of your investment.

    For an HLV-centric architecture, even if you had the extra $3B, you’re at most going to be able to pick a destination and send a few stunt missions to it. Sure it’ll be really exciting, but you’re just going to be littering the Solar Systems with ritualistic monuments to NASA HSF’s hubris, not actually enabling humanity to start leaving the cradle. A depot centric architecture with our current budget would actually get you just as much or more. A depot-centric architecture with $3B more per year would be providing the kind of demand to really strongly incentivize private investment in lower-cost launch technologies (RLVs, gun launch, microwave launch, etc), while also being able to buy down the risks on the technologies you’d need to start really pulling space into humanity’s economic sphere. Stuff like reusable in-space vehicles, aerocapture, ISRU, etc.

    My point is that in order to have a manned HLV-centric exploration program that isn’t a complete and utter waste of money, they need a huge plus-up of $3B per year, and to get rid of that pesky ISS as soon as possible. With a depot-centric exploration program, even if you don’t splash ISS or get a plus-up, you already have an exploration program that’s better. If you get more money it enables you to do even more.

    On its merits, the only thing an HLV-centric architecture gets you that a depot-centric one doesn’t is protecting existing jobs at key lobbyists and campaign contributors.